1. Field of the Invention
The invention relates to industrial storage racks, and particularly racks in which elongated cassettes containing stock such as bars or pipes are inserted in and retrieved from various vertically arranged openings.
2. Description of the Prior Art
One of the concerns in such industrial storage racks is the possibility of incremental slight movement, or "creeping" of the cassettes with respect to the openings as a result of vibrations which occur from time to time. Another potential problem is the possibility of an earthquake or other seismic shock. Since the loads in the cassettes are so great, non-yielding connections between the cassettes and the rack would result in high stresses being inserted on the storage rack structure due to swaying of the loads. This would require the provision of relatively heavy metal sections in the design of the storage rack to withstand such potential forces, greatly increasing the costs of construction.
One of the conventional ways of preventing the creeping action has been to provide mechanical locks at the openings which would retain the cassettes in position. This of course requires a great deal of expense especially where a large number of openings are involved. Another solution attempted in the past has been to provide the rollers in each opening, on which the cassettes are moved in and out, with plain or friction bearings rather than anti-friction bearings. While this reduces the creeping tendency of the cassette, it also greatly increases the required force to insert or retrieve each cassette.